Two doses of the vaccine or placebo will be given to about 50 volunteers in a randomized, double-masked manner. Symptom information will be collected for three days after each dose. Samples of serum and stool will be collected to document excretion of virulent V. cholerae O 139 and to measure the vibriocidal antibody IgG and IgA antitoxin antibody titers in response to immunization.